Cyber bullyig / Invasion on Privacy

Hi good evening, i have a problem. so here's the story, me and my friends have a group chat on Fb. We were talking about this girl who was infamous in our HS. Yes it was below the belt but this is to be expected of Groupchats especially gc of close friends. so out of no where the other party ( the girl who were we talking about. ) sees our gc without our permission. She posted it online, and tags us. many people commented bad stuff and even threats. My side here is that they Private messaged us and i already said sorry and we talked about on blocking each other of Fb. And we did but the other party is persuing a case just in our local town. I dont know what to do since ive already apologized to her about the said issue. Again im really suprised that she found out about our fb message without any of our permission. I wish someone could help lighten the problem. Thank you